Semiconductor device fabrication begins by forming a plurality of semiconductor die on a wafer or a slice of semiconducting material. Each die has one or more integrated circuits formed thereon by a process known as wafer fabrication. In a very simplistic explanation, wafer fabrication involves subjecting a semiconductor wafer to a series of depositions and etches of various conducting and insulating materials to form the circuit(s). Upon the completion of wafer fabrication, the semiconductor die are singulated, or in other words are separated from one another, by cutting the wafer into a plurality of individual semiconductor die. Each die is then assembled by encasing the die in a package body or protective coating and providing a way of electrically accessing the circuit(s) on the die.
As a method of monitoring and controlling the wafer fabrication process, many semiconductor manufacturers incorporate electrical test structures onto the semiconductor wafer. The test structures are formed simultaneously with the semiconductor die, but in general are much simpler circuits. The test structures are used to provide a reasonably accurate interpretation of how well the semiconductor die will perform in view of a few simple test results. In an effort to conserve valuable space on a semiconductor wafer, these test structures are quite small and are most often formed between the semiconductor die. Once wafer fabrication is complete, diagnostic testing is performed on the wafer's test structures to evaluate various electrical characteristics. Upon completion of diagnostic testing, the semiconductor die are cut from the wafer and singulated to prepare the die for subsequent assembly.
One problem that exists in using the test structures described above is that the test structures impede the ability to properly and reliably cut the wafer. Since the test structures are formed between semiconductor die, the test structures lie in the cutting path of the wafer. (Cutting the wafer is also referred to as "scribing" the wafer and thus the cutting path on the wafer, where the test structures are located, is sometimes called the "scribe region.") Because the test structures have already been utilized at this point in fabrication, there is no harm in destroying the test structures during the cutting operation. However, cutting through the structures often involves cutting through large metal regions which are used in the test structures as contact points or probe pads. Probe pads are coupled to the circuits formed within the test structure and are contacted during diagnostic testing by probe needles. The probe pads must be made large enough to ensure accurate placement of the probe needles during testing, thus the size of the probe pads is much larger than the actual circuitry. In cutting through the probe pads, much of the metal which forms the probe pad is torn away by the cutting element, for example a sawing blade. Although destroying the probe pad does not impact a semiconductor device's performance, any metal which is removed from the probe pad may adversely affect the device. For example, the torn metal may become lodged on one of the semiconductor die of the wafer, thereby short-circuiting two of the die which normally are to remain isolated. Therefore, having stray pieces of metal potentially thrown about throughout the assembly of a semiconductor device creates serious reliability concerns.
Because test structures impede the ability to properly and reliably singulate die on a semiconductor wafer, a need exists for an improved semiconductor device, and more specifically, for an improved semiconductor device which has features to aid in cutting metal regions and a process for fabricating the same.